(1) Field of the Invention
The present invention relates to an optical pickup device which records, reproduces and erases information on an optical information storage media such as an optical disc and an optical card.
(2) Description of the Related Art
For highly accurate/high capacity storage media, the range of products to which optical memory technology, which uses optical information storage media with a pit pattern, is applied has expanded to digital audio discs, video discs, document file discs, data files and so on. In optical memory technology, information is stored and reproduced with high accuracy and high reliability in an optical information storage medium using a minutely focused optical beam. These storage and playback processes depend entirely on an optical system. The basic functions of the optical pickup device, which is the main section of the optical system, are divided into: collecting which forms diffraction limit microspots, focus control in the optical system, tracking control for the optical system and detecting pit signals. These functions are realized via a combination of any type of optical system and a photoelectric conversion detection method according to the purpose and usage of the functions. In recent years, in order to miniaturize and make the optical pickup device thinner, a diffraction element (a hologram) is utilized (see for example, Patent Document 1, Japanese Patent Publication No. 2001-176119).
FIG. 1 is a diagram which shows the structure of an optical pickup device which utilizes a conventional diffraction element. The optical pickup device 1000 shown in FIG. 1 records, reproduces and deletes information in the optical information storage medium 1106. For example, the optical information storage medium 1106 is a Compact Disc (CD), a Digital Versatile Disc (DVD), a Blu-ray Disc (BD) or a High Definition DVD (HD-DVD). The optical pickup device 1000 includes a light source 1101A and 1101B, photo detectors 1102A, 1102B, 1102C and 1102D, a diffraction element 1103, an optical path combining unit 1104 and a collection unit 1105.
The light source 1101A is a light source which emits a light at the first wavelength (for example, blue light) 1120, which is light at the first wavelength. The light source 1101B is a light source which emits a light at a second wavelength (for example, red light) 1121, which is light at a second wavelength, which is longer than the first wavelength, as well as a light at the third wavelength (for example, infrared light) 1122 which is light of a third wavelength longer than the second wavelength.
The light at the first wavelength 1120 emitted from the light source 1101A is reflected by the optical path combining unit 1104, collected by the collection unit 1105, irradiated onto the optical information storage medium 1106 and reflected by the optical information storage medium 1106. The light reflected by the optical information storage medium 1106 is collected by the collection unit 1105, passes through the optical path combining unit 1104, enters into the diffraction element 1103 and is diffracted such that the light enters into the photo detectors 1102A and 1102B.
The light at the second wavelength emitted from the light source 1101B is collected by the collection unit 1105, irradiated onto the optical information storage medium 1106 and reflected by the optical information storage medium 1106. The light reflected by the optical information storage medium 1106 is collected by the collection unit 1105, enters the diffraction element 1103, and is diffracted such that the light is selectively introduced into the photo detectors 1102A and 1102C. The light at the third wavelength 1122 emitted from the light source 1101B is collected by the collection unit 1105, irradiated onto the optical information storage medium 1106 and reflected by the optical information storage medium 1106. The light reflected by the optical information storage medium 1106 is collected by the collection unit 1105, enters the diffraction element 1103, and is diffracted such that the light is introduced selectively into the photo detectors 1102A and 1102D.
In other words, when the diffracted light on the right side of the diagram is defined by the diffraction element 1103 as − (minus), and the light diffracted on the left side as + (plus), then the + first-order diffracted light within the reflected light of the first through third wavelengths enters the photo detector 1102A. As for the − first-order diffracted light, diffracted light at the first wavelength enters the photo detector 1102B, diffracted light at the second wavelength enters the photo detector 1102C and diffracted light at the third wavelength enters the photo detector 1102D. A signal is outputted according to the amount of received light from the photo detectors 1102A through 1102D.
However, in a conventional optical pickup device 1000, since unnecessary diffracted light diffracted by the diffraction element 1103 enters the semiconductor board on which the photo detectors 1102A through 1102D are formed, there is the problem that stray light will be generated. The signal used for data storage, playback and deletion in the optical information storage medium 1106 deteriorates due to the stray light.